Flooding events can be precipitated by natural and manmade inputs. These events can be particularly challenging for buildings and infrastructure located at or near a body of water. Transportation systems or buildings in these areas that are below the normal waterline are particularly vulnerable. Severe storms with high tidal surges or flash floods, rising sea levels, and seismic activity are some of the challenges posed by nature. Accidents, terrorism, and mechanical failures are manmade threats that can cause flooding, or magnify flooding from natural events.
Many subway and vehicular tunnels that operate below waterline around the world have experienced flooding. Hurricane Sandy was particularly devastating to New York City in 2012 because a significant portion of the subway system was flooded and economic losses were unprecedented. Water entrance points included subway portals, stairwell entrance points, ventilation shafts, emergency exits, and elevator shafts. Vehicular tunnels were also flooded, as well as many buildings. This was one of the worst flooding events in history, but it was just one in a string of events in subway systems in major cities around the world.
There are many types of flood mitigation systems available commercially. This includes Flexible Flood Mitigation Devices, stop logs, and flood doors. These are designed to withstand significant hydrostatic pressures (up to tens of feet of water) and do so with rigid components and mechanisms to deploy them. These systems often require significant modification to the infrastructure during installation, a considerable amount of storage space, frequent maintenance, and are costly to install because of the impact on the system. Because of this, they are often found to be unacceptable in transit and other applications.
Textile & membrane based Flexible Flood Mitigation Devices offer significant benefits over the rigid devices. Most notable is the ability to pack the material into a small volume for storage. This not only allows the Flexible Flood Mitigation Device to be stored in a small volume that is easily fit into existing spaces, but it minimizes the modifications required on the infrastructure to install it. The membrane door itself is shaped to minimize stress in the door (governed by pressure multiplied by radius of curvature). The door is attached to tracks with a “deadman” which guides deployment and also seals the door when the door is tensioned. The deadman is an assembly which is larger than the slot in the guide rail and therefore prevents extraction when the door is tensioned by water pressure. The base of the membrane door has a plate to guide deployment and support an elastomeric seal that seals that edge of the door. The membrane door can be packed via rolling or folding, and can be deployed manually or automatically from a spool with a motor. The design has very few moving parts and requires little to no regular maintenance, and is survivable in many harsh environments.